Embodiments of the present disclosure generally relate to neurostimulation (NS) systems, and more particularly to systems and methods for analyzing evoked waveforms to determine a neuronal system response.
NS systems include devices that generate electrical pulses and deliver the pulses to nerve tissue to treat a variety of disorders via one or more electrodes. For example, spinal cord stimulation has been used to treat chronic and intractable pain. Another example is deep brain stimulation, which has been used to treat movement disorders such as Parkinson's disease and affective disorders such as depression. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of electrical pulses depolarize neurons and generate propagating action potentials into certain regions or areas of nerve tissue. The propagating action potentials effectively mask certain types of physiological neural activity, increase the production of neurotransmitters, or the like.
During stimulation by the NS systems, evoked potentials are emitted from the stimulated nerve tissue. The evoked potential signals may be generated by neuronal transmembrane currents of neurons activated following or in response to the NS. The simultaneous activation of multiple neurons generates a signal of sufficient amplitude for recording. The evoked potential signals propagate within the population of sensory nerve fibers through subsequent orthodromic or antidromic propagation from the excitation site.
It has been proposed that the neural signals recorded during electrical stimulation may provide feedback for adjustment of stimulation parameters in neuromodulation devices. For example, local field potentials (LFPs) are signals that are present within the brain and can be recorded from a deep brain stimulation (DBS) lead. It has been proposed that symptoms of movement disorders may be correlated to the LFP signal magnitude at specific signal frequencies, such as a beta band (13-35 Hz) in Parkinson's disease. Additionally, evoked potentials can be measured from spinal cord stimulation (SCS) leads. The amplitude of the evoked potential is related to the number of neurons in the spinal cord activated by SCS, and thereby indicates changes in the response to stimulation caused by movement of the SCS lead or other reasons.
However, recording neural activity can be challenging due to biological and external noise sources that obscure or confound recording of the signal of interest. Consequently, changes in the signal of interest may not be readily discernible, due to subtle shifts in amplitude, phase, or frequency. Moreover, the changes in the signal may be complex. For example, a change in signal amplitude at one frequency may correspond to a change in phase at a second frequency (“phase-amplitude coupling”).
A need exists to overcome the shortcomings of conventional approaches to identify the neuronal system response to stimulation.